Generally, in the process for making paper, incremental amounts of liquid are removed from a slurry of pulp in a succession of steps. In a first forming step, the slurry is deposited on a porous fabric which drains much of the liquid by gravity and suction, and leaves a wet web of solids on the fabric surface. In a later pressing step, the wet web is compressed between fabrics to remove additional liquid. In a still later, drying step more liquid is removed by evaporation, usually by supporting the web by dryer fabrics so that the web is in contact with large diameter, smooth, heated rolls.
The papermaking process places considerable demands on the fabrics used in each process step. The fabrics should be structurally strong, flexible, abrasion resistant, chemical resistant and able to withstand the high temperatures to which they can be exposed for extended times.
One major improvement in the technology of papermaking fabric has been the introduction of synthetic polymer monofilament. A suitable polymer must provide a yarn having physical properties which satisfy the requirements of automated fabric manufacturing and the demands of papermaking.
Monofilaments have been made from such polymers as polyethylene terephthalate (PET) and polyphenylene sulfide (PPS). The physical properties of a monofilament affect its suitability for use in a papermaking fabric. PET has good dimensional stability, reasonable resistance to abrasion and is moderately priced; however, it has marginal hydrolytic stability and it degrades rapidly in the presence of a caustic solution. PPS monofilament has excellent hydrolytic and thermal stability but is very expensive and relatively brittle.
It is desired to provide a papermaker's fabric having improved caustic, hydrolysis and abrasion resistance.